Method of making an electromagnetic interference shield device

ABSTRACT

A method of packaging a device is disclosed. In one embodiment, a substrate including a common voltage plane and a mounting region is provided, with the device mounted to the mounting region. An electrically conductive dam structure is disposed on the surface of the substrate with the electrically conductive dam structure being electrically coupled to the common voltage plane and circumscribing a perimeter of the mounting region. An electrically insulating encapsulant at least partially fills a pocket defined by the substrate and the electrically conductive dam structure, the electrically insulating encapsulant contacting the electrically conductive dam structure. An electrically conductive encapsulant is provided that overlies the electrically insulating encapsulant, the electrically conductive encapsulant being coupled to the electrically conductive dam structure.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of an application entitled“Electromagenetic Interference Shield Device and Method,” which wasassigned application Ser. No. 09/141,936, was filed on Aug. 28, 1998,now U.S. Pat. No. 6,092,281 and is incorporated herein by reference inits entirety.

FIELD OF THE INVENTION

The present invention relates to packaging technology, and morespecifically, to an electromagnetic interference shield package andmethods for providing and using the electromagnetic interference shieldpackage.

BACKGROUND OF THE INVENTION

Electromagnetic interference (EMI) is the impairment of a wantedelectromagnetic signal by an electromagnetic disturbance. Eachelectronic component operates using a flow of charge carriers, the flowinducing a surrounding electromagnetic field. This surroundingelectromagnetic field may cause sufficient noise within surroundingelectronic components that the performance of the surroundingelectromagnetic components is degraded. EMI is a particular problem incellular phones in which an antenna emits radio frequencies (RF) whichcould affect the other circuitry operating in the phone. In order toisolate an electronic component from EMI, EMI shielding has beenrecently developed.

Lin (U.S. Pat. No. 5,436,203) discusses an EMI shielded device. FIG. 1is a cross-sectional view of a similar EMI shielded device. In FIG. 1,an electrically insulating encapsulant 38 mechanically protects asemiconductor die 32. The electrically insulating encapsulant 38 isconstrained by a dam structure 40 so as not to encapsulate electricallyconductive reference pads 18. Reference pads 18 are electricallyconnected to the reference plane 22 by electrically conductive vias 20.An electrically conductive encapsulant 42 is dispensed over the firstencapsulant and is in contact with the reference pads 18. Theelectrically conductive encapsulant 42 is constrained by a second damstructure 44.

The shielding of device 32 requires the fabrication of two separate damstructures 40 and 44. This requires two separate process steps, one stepfor the deposition of each dam structure 40 and 44. Furthermore, thesize of the package 30 is much larger than the size of the device 32because a dam structure 40 must surround device 32 while a separate damstructure 44 surrounds the dam structure 40. This double dam structureresults in a large footprint of package 30 on a printed circuit board.

It is desirable to reduce the number of process steps in packaging asemiconductor device. It is also desirable to reduce the package sizerelative to the device size.

SUMMARY OF THE INVENTION

In accordance with the present invention, a package for a device isdescribed. The package includes a substrate having a common voltageplane and a mounting region. The device is mounted to the mountingregion. An electrically conductive dam structure is disposed on theupper surface of the substrate. The electrically conductive damstructure is electrically coupled to the common voltage plane andcircumscribes a perimeter of the mounting region. An electricallyinsulating encapsulant at least partially fills a pocket defined by thesubstrate and the electrically conductive dam structure. Theelectrically insulating encapsulant contacts the electrically conductivedam structure. An electrically conductive encapsulant overlies theelectrically insulating encapsulant and is coupled to the electricallyconductive dam structure.

The package in accordance with the present invention shields the devicefrom EMI such as radio frequency (“RF”) interference using only one damstructure. Since a double dam structure of the prior art uses anadditional dam structure surrounding a primary dam structure, thepackage of the present invention is substantially smaller (e.g., by 10to 20 percent or more) compared to the double dam structure package ofthe prior art.

In accordance with the present invention, a method of packaging a deviceis described as follows. The method includes providing a substratehaving a common voltage plane and a mounting region. The device ismounted to the mounting region. The method includes providing anelectrically conductive dam structure disposed on the upper surface ofthe substrate. The electrically conductive dam structure is electricallycoupled to the common voltage plane and circumscribes a perimeter of themounting region. The method includes providing an electricallyinsulating encapsulant which at least partially fills a pocket definedby the substrate and the electrically conductive dam structure. Theelectrically insulating encapsulant contacts the electrically conductivedam structure. The method includes providing an electrically conductiveencapsulant that overlies the electrically insulating encapsulant andwhich is coupled to the electrically conductive dam structure.

The method of fabricating in accordance with the present inventionresults in an EMI shield device in which only one dam structure isfabricated. The number of dam structures in the conventional double damstructure package may be two. Each dam structure deposition requires aseparate process step. Therefore, the method of the present inventionreduces the number of steps required to fabricated an EMI shield device.

In accordance with the present invention, a method of using a packageincludes applying a common voltage to the common voltage plane. Acontext for the common voltage plane is as follows. The device ismounted to a mounting region of the substrate. An electricallyconductive dam structure is disposed on the surface of the substratearound a periphery of the mounting region. The electrically conductivedam structure is electrically coupled to the common voltage plane. Theelectrically insulating encapsulant at least partially fills a pocketdefined by the substrate and the electrically conductive dam structure.An electrically conductive encapsulant overlies the electricallyinsulating encapsulant. The electrically conductive encapsulant beingelectrically coupled to the electrically conductive dam structure.

The method of using the device in accordance with the present inventionallows for the use of a device that is EMI shielded and is smaller thanconventional EMI shielded devices.

These and other objects, features and advantages of the presentinvention will be more readily apparent from the detailed description ofthe various embodiments set forth below taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an EMI shielded device in accordancewith the prior art.

FIG. 2 is an isometric view of a package having a device mounted to asurface of a substrate during packaging in accordance with the presentinvention.

FIG. 3 is an isometric view of the package of FIG. 2 having anelectrically conductive dam structure dispensed around a periphery ofthe device to define a pocket with the substrate.

FIG. 4 is a cross-sectional view of the package of FIG. 3 alongcross-section line 4—4 of FIG. 3.

FIG. 5 is a cross-sectional view of a package having a flip chip mounteddevice in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several elements in the following figures are substantially similar.Therefore similar reference numbers are used to represent substantiallysimilar elements.

FIG. 2 is an isometric view of a package 200 having a device 210 mountedto an upper surface 221 of a substrate 220 during packaging inaccordance with the present invention. Device 210 may be a semiconductordie which may contain circuitry sensitive to EMI.

Substrate 220 has contact regions, such as bond pads 222 a and 222 b,formed on upper surface 221. Device 210 has corresponding contactregions, such as bond pads 223 a and 223 b, coupled to circuitry (notshown) within device 210. Leads, such as bond wires 224 a and 224 b,electrically couple bond pads 223 a and 223 b to respective bond pads222 a and 222 b. Bond pads 222 a and 222 b are electrically coupled tocorresponding solder balls 242 (FIG. 4) on the lower surface 244 ofsubstrate 220 (FIG. 4). Alternatively, device 210 is electricallyconnected to substrate 220 in a leadless fashion such as is described indetail hereinafter with reference to FIG. 5.

Substrate 220 has a common voltage contact region, such as a ground viasurface 225, on upper surface 221. Ground via surface 225 may beconnected to a common voltage plane, such as a ground plane 236.

FIG. 3 is an isometric view of package 200 having an electricallyconductive dam structure 228 dispensed around a periphery of device 210to define a pocket 230 with substrate 220. Electrically conductive damstructure 228 may be deposited as a high viscosity liquid around theperimeter of device 210 using, for example, a dispense system such as anMRSI 375-3S dispenser produced by MRS Technology, Inc., located at 10Elizabeth Drive, Chemlsford, Mass. Electrically conductive dam structure228 circumscribes device 210, bond pads 222 a and 222 b and bond wires224 a and 224 b. Electrically conductive dam structure 228 is disposedover, and in contact with, ground via surface 225.

Electrically conductive dam structure 228 is composed of an electricallyconductive material such as, for example, an epoxy resin withelectrically conductive fillers. The electrically conductive fillers maybe, for example, carbon (approximately 5% by weight of the resincompound) and silver (approximately 20% by weight of the resin compound)Such an epoxy resin with conductive fillers may be supplied by DexterElectronics Materials, 9938 Via Pasar, San Diego, 92126 under materialidentification number QMIDW1193-588.

However, one skilled in the art will recognize that the filler to resinweight ratio may be altered to obtain a desired electricallyconductivity. For example, the filler to resin weight ratio may varyfrom 5% or less to 50% or more. Package 200 also includes otherpackaging elements that are not shown in FIG. 3 for clarity. Thesepackaging elements are shown and described with reference to FIG. 4.

FIG. 4 is a cross-sectional view of package 200 along cross-section line4—4 of FIG. 3. Ground via 227 connects ground via surface 225 to groundplane 236. An electrically insulating encapsulant 232 (e.g., epoxy) isdeposited within the pocket 230 defined by the electrically conductivedam structure 228 and substrate 220 using, for example, an MRSI 375-3Sdispense system. The electrically insulating encapsulant 232 at leastpartially fills the pocket such that device 210 and bond wires 224 a and224 b are mechanically supported, protected, and electrically insulated.

An electrically conductive encapsulant 233 covers the electricallyinsulating encapsulant 232 and is electrically connected to electricallyconductive dam structure 228. The electrically conductive encapsulant233 is deposited, using, for example, the MRSI 375-3S dispense system,such that the electrically conductive encapsulant 233 is electricallycoupled to electrically conductive dam structure 228. The electricallyconductive encapsulant may be of a material similar to electricallyconductive dam structure 228 and may be of such a thickness that thesheet resistance is approximately 1000 ohms/cm².

During operation of device 210, a common voltage supply, such as ground,may be optionally coupled to ground plane 236. This optional coupling isrepresented by a switch 240 being closed. However, during packaging, thevoltage level on ground plane 236 may also float (switch 240 is open).The common voltage supply 238 is connected to ground plane 236, as shownin FIGS. 4 and 5, through a via 250. Via 250 electrically connects theground plane 236 to solder ball 246, which acts as an input pin for thevoltage supplied by common voltage supply 238. Ground plane 236, groundvia 227, electrically conductive dam structure 228, and electricallyconductive encapsulant 233 are all at a common voltage (either byfloating or being coupled to the common voltage source 238) andsubstantially encapsulate device 210. Device 210 is thus substantiallyshielded from EMI.

FIG. 5 is a cross-sectional view of a package 500 having a flip chipmounted device 510 in accordance with the present invention. Package 500is structured similar to package 200 of FIGS. 2-4 except that a flipchip mounted device 510, not adhesively attached and wire bonded device210, is mounted to upper surface 221 of substrate. Bond wires 224 a and224 b are absent because flip chip mounted device 510 has terminals 523a and 523 b directly connected to terminals 522 a and 522 b on substrate220. Terminals 522 a and 522 b are electrically coupled to correspondingsolder balls 242 on the lower surface 244 of substrate 220.

A method of manufacturing package 200 is now described. The stepsdescribed below are not chronologically related to each other unlessexpressly described below.

Device 210 is mounted to a mounting region 254 (FIG. 4) of substrate220. The “mounting region” is defined as the region to which device 210has been, or is to be, mounted. Electrically conductive dam structure228 is deposited around the outer periphery of mounting region 254.After electrically conductive dam structure 228 is deposited,electrically conductive dam structure 228 may be exposed to ultra violetlight (e.g., 310 nanometers wavelength) until electrically conductivedam structure 228 is gelled.

After device 210 is mounted and electrically conductive dam structure228 is deposited, electrically insulating encapsulant 232 is depositedinto pocket 230 so as to at least partially fill pocket 230 and so as tocover bond wires 224 a and 224 a and device 210. After depositing theelectrically insulating encapsulant 232, electrically insulatingencapsulant 232 may also be gelled by, for example, exposure to ultraviolet light for 30 seconds.

After, electrically conductive dam structure 228 and electricallyinsulating encapsulant 232 are deposited, electrically conductiveencapsulant 233 is deposited over electrically insulating encapsulant232 in such a way that electrically conductive encapsulant 233 iselectrically coupled to electrically conductive dam structure 228.

Electrically conductive dam structure 228, electrically insulatingencapsulant 232 and electrically conductive encapsulant 233 may be curedafter depositing electrically conductive encapsulant 233. Curing mayoccur by exposure to a temperature of approximately 80 degrees Celsiusfor 20 minutes followed by exposure to a temperature of approximately150 degrees Celsius for 40 minutes. Package 500 of FIG. 5 is made usingsubstantially the same technique as described above in reference topackage 200 of FIG. 4, except that device 510 of FIG. 5 is mounted tosubstrate 220 using a flip chip interconnection.

The above described packages 200 and 500 have only one dam structurecompared to the two of the conventional double dam structure package.This eliminates the need to have a separate processing step fordepositing a second dam structure. Therefore, the number of processingsteps to package device 210 (or 510) is reduced compared to theconventional double dam structure package. Furthermore, the size of thepackage 200 (or 500) is reduced compared to the double dam structures ofthe prior art EMI shielding package because a second dam structure isnot deposited around electrically conductive dam structure 228. Thisreduces the size of the package (e.g., by 10 to 20% or more) compared tothe double dam structure package.

Having thus described the various embodiments, persons skilled in theart will recognize that changes may be made in form and detail withoutdeparting from the spirit and scope of the invention.

For example, although one ground via 227 is described, two or moreground vias will suffice. Even zero ground vias are sufficient if theelectrically conductive encapsulant 233 or electrically conductive damstructure 228 is independently coupled to a common voltage supply. Zeroground vias are also sufficient if the dam structure 228 is not coupledto a voltage supply, but is permitted to float.

Although only one device 210 is shown circumscribed by electricallyconductive dam structure 228, two or more devices may be circumscribedby electrically conductive dam structure 228 to be EMI shielded.Although only two leads, bond wires 224 a and 224 b, are described,device 210 may have many more leads.

Thus the invention is limited only by the following claims.

I claim:
 1. A method of packaging a device comprising: providing asubstrate including a common voltage plane and a mounting region, thedevice mounted to the mounting region; providing an electricallyconductive dam structure disposed on a surface of the substrate, theelectrically conductive dam structure electrically coupled to the commonvoltage plane and circumscribing a perimeter of the mounting region;providing an electrically insulating encapsulant at least partiallyfilling a pocket defined by the substrate and the electricallyconductive dam structure, the electrically insulating encapsulantcontacting the electrically conductive dam structure; and providing anelectrically conductive encapsulant overlying the electricallyinsulating encapsulant, the electrically conductive encapsulant coupledto the electrically conductive dam structure; curing the electricallyconductive encapsulant, the electrically insulating encapsulant, and theelectrically conductive dam structure; floating a voltage on the commonvoltage plane.
 2. The method of claim 1, wherein said providing theelectrically conductive dam structure on the substrate comprisesdepositing an electrically conductive epoxy compound in a form of a damstructure on the substrate.
 3. The method of claim 2, wherein saidproviding the electrically insulating encapsulant comprises depositingan insulating epoxy within the pocket defined by the device, thesubstrate and the electrically conductive dam structure.
 4. The methodof claim 1, wherein said providing the electrically insulatingencapsulant includes constraining said electrically insulatingencapsulant within said electrically conductive dam structure.
 5. Amethod of making a package for a device, the method comprising:providing a substrate having first and second opposed sides, with anelectrically conductive plane disposed therebetween and an electricallyconductive via extending from the first side to the electricallyconductive plane; mounting the device on the first side of the substrateand electrically connecting the device to the substrate; applying anelectrically conductive dam on the first side of the substrate so as tooverlay the via, surround a portion of the first side of the substrate,and define a pocket, wherein the device is within the pocket; andapplying an electrically insulating encapsulant over the device andwithin the pocket; applying an electrically conductive encapsulant ontothe electrically insulating encapsulant, wherein the electricallyconductive encapsulant is electrically connected to the electricallyconductive dam.
 6. The method of claim 5, wherein the electricallyinsulating encapsulant is applied so as to contact the electricallyconductive dam.
 7. The method of claim 6, wherein the substrate includesan electrically conductive path between the plane and the second side ofthe substrate, and further comprising mounting at least one solder ballon the second side of the substrate, wherein said solder ball is inelectrical communication with the path.
 8. The method of claim 5,wherein the electrically insulating encapsulant is applied so as tocontact the electrically conductive dam.
 9. The method of claim 8,wherein the device is mounted in a flip chip style.
 10. The method ofclaim 8, further comprising electrically connecting at least one bondwire between the device and the substrate.